This is the first systematic examination of the business of mass migration travel across the North Atlantic during the period of unprecedented globalization prior to World War I. It explicates the reinforcing interests and actions of the oceanic shipping lines, their migrant customers, and contemporary government authorities, in coping with the substantial risks of mass physical relocation, particularly those due to cyclical economic recessions, and in keeping migration safe, smooth and largely self-regulated. In a comprehensive analysis backed up by extensive and consistent statistics, it details the motives and mechanisms by which these eleven million Europe-born migrants made nineteen million ocean crossings on eighteen thousand voyages of several hundred large steamships, generating hundreds of millions of dollars in revenues for these steamship lines during the pivotal peak years of early twentieth century migration between Europe and America, and it describes how this long-lived long-distance travel business operated as the crucial common denominator of the greatest and most ethnically diverse mass transoceanic relocation ever.